Tragedy at
Armero
When the Nevado del Ruiz volcano erupted on November 13,
1985, a lahar caused by the eruption swept down the
Lagunillas River and killed 22,000 people in the town of
Armero.

The eruption was expected, monitoring was ongoing, and
officials had been warned that an eruption was likely. A
hazard map was available that correctly portrayed the
risk to Armero.

Arial photo of the
lahar that destroyed the town of Armero.

During a previous eruption in 1845, a
lahar had swept down the mountain, killing approximately
1,000 people at the present-day location of Armero. With
this evidence, the tragedy at Armero should not have
happened. A failure in disaster communications was
largely to blame.

A Success Story
in Iceland
A volcanic eruption on September 29, 1996, beneath the
Vatnajoekull icecap on Iceland melted about three cubic
kilometers of ice. Monitoring equipment detected the
event, and through past experience, scientists were able
to predict that a large outburst flood would occur along
the Skeidar River. When the outburst, or
"jokulhlaup," occurred on November 5, the
Skeidar briefly became the second largest river in
the world. Although damages to bridges, roads, and
utilities totaled some $15 million, no lives were lost.

Monitoring Mt.
St. Helens
When Mt. St. Helens awoke on March 20, 1980, with a small
earthquake near the mountain, volcanologists responded
with increased monitoring. As seismicity, gas emissions,
and a growing bulge on the flank of the volcano were
accompanied by small steam and ash eruptions, monitoring
was increased and restricted zones around the mountain
were defined.

As luck would have it, a map for Mt. St. Helens had
recently been completed, and this was used for many
decisions. Some zones were totally evacuated, while
restricted access was allowed to others. Reservoir levels
were decreased, and a well-defined information flow was
put into place. When the cataclysmic eruption occurred on
May 18, it caused widespread devastation and the loss of
68 lives. The economic loss exceeded $1.8 billion.
Without hazard maps and monitoring, both human and
economic losses would have been much greater.